Reduction of dielectric losses through use of organoclay in semiconductor or insulator compositions

ABSTRACT

Organoclays are added to semiconductive compositions to provide a reduction in the dielectric losses of layered composites in which the semiconductive layer contains species which could migrate into the insulation and result in undesirably high dielectric losses. The invention semiconductive compositions provide improved performance in power cable applications.

FIELD OF THE INVENTION

The present invention relates generally to reducing dielectric lossesand more specifically to formulation of semiconductor or insulatorcompositions for improved performance in power cable applications andthe like.

BACKGROUND OF THE INVENTION

Typical power cables, including those for small appliances to outdoorstation-to-station power cables, often comprise one or more conductorsin a core that may be surrounded by one or more layers. These layers mayinclude one or more of the following: a first polymeric semi-conductingshield layer; a polymeric insulating layer; a second polymericsemi-conducting shield layer; and optionally, a metallic tape shield;and a polymeric jacket.

Semiconductive compositions may include resin components which are knownto exhibit high dielectric losses when used in insulating compositions.While this may not be a problem in a semiconductive composition, speciesmigration from the semiconductive layer into an adjacent insulationlayer can lead to increased dielectric losses of the layered composite.Reduction in the migration of the diffusing species from thesemiconductive layer into the insulation, or enhanced solubilization ofthis species within the semiconductive layer is expected to yieldimproved dielectric properties of the layered composite. This would beuseful in electrical applications such as power cables.

Some elastomeric components used in semiconductive shield formulationsmay contain species that diffuse into the insulation, which leads toenhanced dielectric losses in power cables (especially at temperaturesabove the 90° C. normal operating temperature rating of the cable).

The present invention provides a means to enable the use of a class ofelastomeric materials in the semiconductive compositions of the cabledesign that would otherwise lead to much higher cable dielectric lossesin shorter aging times.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to the use of particular organoclays in asemiconductive layer and/or an insulator layer to provide reduceddielectric losses. Improved dielectric performance has been demonstratedby addition of a small amount of organoclay in the semiconductivecomposition or in the insulator. The increase in dielectric losses ofthe insulation adjacent to the semiconductive layer containingorganoclay was reduced significantly after a similar period of thermalaging.

In one embodiment, the invention is a structure comprising asemiconducting layer comprising a first material that comprises a firstpolymeric resin and a conductive filler and an insulating layercomprising a second material that comprises a second polymeric resin,wherein the semiconducting layer and the insulating layer are at leastpartially in physical contact with each other, wherein at least one ofthe first material and the second material comprise an organoclay andwherein the first polymeric resin and the second polymeric resin may bethe same or different.

In another embodiment the invention is an article comprising aninsulating layer that comprises a composition comprising at least onepolymeric resin and at least one organoclay.

In one embodiment the invention is a cable comprising a core comprisingone or more conductors; a semiconducting layer comprising a firstmaterial that comprises a first polymeric resin and a conductive fillerand, an insulating layer adjacent to the semiconductor layer, theinsulating layer comprising a second material that comprises a secondpolymeric resin, wherein the semiconducting layer and the insulatinglayer directly or indirectly surround the core, wherein at least one ofthe first material and the second material comprise an organoclay andwherein the first polymeric resin and the second polymeric resin may bethe same or different.

In one embodiment the ratio of AC dielectric losses of a comparativestructure (that is identical to the structure except that thecomparative structure lacks Organoclay), to the structure is greaterthan 1.5.

In one embodiment the invention is an article comprising an insulatinglayer that comprises a composition comprising at least one polymericresin and at least one Organoclay, wherein the polymeric resin has an ACdielectric loss at least 1.5 times greater than the AC dielectric lossof the layer.

In one embodiment the invention is an insulator comprising a polymericresin and an organoclay, wherein the ratio of AC dielectric loss of thepolymeric resin to the AC dielectric loss of the insulator is at least1.5

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph showing dissipation factors of insulation layers.

FIG. 2 is a graph showing dissipation factors of insulators removed fromcontact with various semiconductive compositions.

FIG. 3 is a graph showing dissipation factors after aging in contactwith semiconductors of various compositions.

FIG. 4 is a graphical representation dissipation factors in EPDM resins.

FIG. 5 is a graph showing dissipations factors of various compositions.

DETAILED DESCRIPTION OF THE INVENTION

The present invention enables the use of a class of elastomericmaterials in the semiconductive compositions of the cable design thatwould otherwise lead to much higher cable dielectric losses in shorteraging times. Organoclays have been used in the preparation ofsemiconductive compositions or in insulation compounds to reduce themigration of species from the semiconductive composition into adjacentinsulating layers, where they would otherwise contribute to significantincreases in dielectric losses of the layered composite. The result is areduction in the dielectric losses of layered composites in which thesemiconductive layer contains species which could migrate into theinsulation and result in undesirably high dielectric losses. Similarly,the use of organoclays may also be advantageous in insulations that maynot need adjacent semiconductive layers. In this case, the lossydielectric species may be inherent within the insulation and the use oforganoclay helps to mitigate the lossy nature of the insulation.

The term “insulator” or “insulation” as used herein means any materialthat resists, or prevents, the flow of electricity through the material.The insulators of the current invention normally comprise polymericresins or compounds, as described below. Such polymeric resins typicallyhave inherent insulating properties.

The term “semiconductor” or “semiconductive” as used herein means anymaterial or property respectively that is intermediate in electricalconductivity between conductors and insulators, through which conductiontakes place by means of holes and electrons. The semiconductors of thecurrent invention normally are compositions of polymeric materials witha conductive filler, as described below.

A wide variety of polymeric materials have been utilized as electricalinsulating and semi-conducting shield materials for power cables and inother numerous applications. In order to be utilized in services orproducts where long term performance is desired or required, suchpolymeric materials, in addition to having suitable dielectricproperties, must also be enduring and must substantially retain theirinitial properties for effective and safe performance over many years ofservice. For example, polymeric insulation utilized in building wire,electrical motor or machinery power wires, underground powertransmitting cables, fiber optic telecommunication cables, and evensmall electrical appliances must be enduring not only for safety, butalso out of economic necessity and practicality. Non-enduring polymericinsulation on building electrical wire or underground transmissioncables may result in having to replace such wire or cable frequently.

Common polymeric compositions for use in electrical devices are madefrom polyvinylchloride (PVC), polyethylene homopolymers and copolymers,ethylene/vinyl acetate (EVA) copolymer or ethylene-propylene elastomers,otherwise known as ethylene-propylene-rubber (EPR). Each of thesepolymeric compositions is often undesirable for one or more reasons. Forinstance, the use and disposal of PVC is often heavily regulated forenvironmental reasons and a suitable substitute material for use inelectrical insulation would be desirable.

Polyethylene is generally used neat without a filler as an electricalinsulation material. There have been attempts in the prior art to makepolyethylene-based polymers with long term electrical stability. Forexample, polyethylene has been crosslinked with dicumyl peroxide inorder to combine the improved physical performance at high temperatureand have the peroxide residue function as an inhibitor of thepropagation of electrical charge through the polymer, a process known astree formation. Unfortunately, these residues are often degraded at mosttemperatures they would be subjected to in electrical power cableservice.

In contrast to polyethylene, EPR is generally used as an electricalinsulator in combination with a high level of filler (typically about 20to 50 percent by weight). Unfortunately, this combination of EPR andfiller usually gives poor dielectric properties.

The semi-conductive compositions of the devices of the present inventiontypically comprise a polymer or polymer blend and a conducting filler torender the composition semi-conducting. The most common fillers forsemi-conductive compositions are carbon black and graphite. The amountof filler will vary depending on the type of filler and othercomponents. Generally, the filler will comprise from about 10 to about55 weight percent of the filled semi-conductive composition. Preferably,the filler will comprise from about 20 to about 45, more preferably fromabout 30 to about 40, weight percent of the filled semi-conductivecomposition. If desired, a plurality of neutral wires which are usuallymade of copper may be embedded in or wrapped around the layer ofsemi-conducting insulation shielding in the form of a concentric helicesaround the insulated cable.

As used herein, an organoclay (also known as organophilic clay) isgenerally an organopolysilicate. Organoclays are made by reacting, viaion exchange mechanisms, organocations with natural clays. Theorganocations exchange with the natural interlayer cations of the clayto generate organophilic surfaces while maintaining a lamellar structuresimilar to the natural clay. Typically, the organocations are quaternaryammonium compounds. Common examples of organoclays include clays, suchas kaolin or montmorillonite, to which organic structures have beenchemically bonded. Organoclays used in the invention may have an excessof quaternary ammonium compounds. More details of producing organoclayscan be found in e.g. U.S. Pat. No. 5,780,376. Organoclays are alsocommercially available, such as the CLOISITE® line of naturalmontmorillonite clays modified with quaternary ammonium salts availablefrom Southern Clay Products, Inc. The organoclay is typically added at alevel of up to about 3 wt % based on the total weight of the polymericresins in the compound. In some embodiments, the amount of organoclayranges from about 1 wt % to about 3 wt %, based on the total weight ofthe resins in the compound.

The organoclay can be incorporated into the insulator or semiconductorcompositions by any method that provides adequate distribution andmixing. Typically, the organoclay is melt mixed with the resins in amelt mixer, extruder or similar equipment. Techniques for melt blendingof a polymer with additives of all types are known in the art and cantypically be used in the practice of this invention. Typically, in amelt blending operation useful in the practice of the present invention,the polymer resin is heated to a temperature sufficient to form apolymer melt and combined with the desired amount of the organoclay in asuitable mixer, such as an extruder, a Banbury Mixer, a Brabender mixer,or a continuous mixer. The composite may be prepared by shearing thepolymer and the organoclay in the melt at a temperature equal to orgreater than the melting point of the polymer. Mechanical shearingmethods are employed such as by extruders, injection molding machines,Banbury type mixers, or Brabender type mixers. Shearing may be achievedby introducing the polymer melt at one end of an extruder (single ordouble screw) and receiving the sheared polymer at the other end of theextruder. The temperature of the melt, residence time of the melt in theextruder and the design of the extruder (single screw, twin screw,number of flights per unit length, channel depth, flight clearance,mixing zone) are several variables which control the amount of shear tobe applied.

Alternatively, the polymer may be granulated and dry-mixed with theorganoclay and thereafter, the composition heated in a mixer until thepolymer resin is melted to form a flowable mixture. This flowablemixture can then be subjected to a shear in a mixer sufficient to formthe desired composite. The polymer may also be heated in the mixer toform a flowable mixture prior to the addition of the organoclay. Theorganoclay and polymer resin are then subjected to a shear sufficient toform the desired composite.

The current invention is useful in preventing long-term dielectriclosses in structures having a semiconductor layer adjacent to aninsulating layer, in particular wires and cables.

EXAMPLES

A laboratory method has been developed to thermally age (1 week at 140°C.) a “sandwich” prepared from one layer of insulation and another ofthe semiconductive composition, and then to separate the layers fordielectric analysis of the insulating layer only. Differences in thedielectric losses of the insulation layer can thereby be attributed todifferences in the semiconductive formulation against which theinsulation layer was in contact during the aging process. The losses arealso compared to insulation layers that are thermally aged with noexposure to semiconductor layers, insulation layers removed fromsemiconductor compositions without aging, and insulation layers removedfrom semiconductors after aging in which the semiconductor compositioncontained no elastomer. Two different insulation formulations areemployed to demonstrate that the observed increase in dielectric lossesis not related to the tree-retardant insulation formulation or specificinteractions of that formulation with elements of the semiconductivecompositions. The test formulations are shown in Table 1 and the testresults are shown in Tables 2A and 2B, and FIGS. 1 and 2.

Procedure 1 Mold a 50-mil semiconductor plaque and cure at 180° C. underpressure for 16 minutes. 2 Mold a 30-mil insulation plaque and cure at180° C. under pressure for 16 minutes. 3 Prepare asemiconductor-insulation layered plaque in press at 180° C. under lowpressure. Leave at temperature for 5 minutes, just to allow time forintimate contact. 4 Condition layered plaque in a vacuum oven at 60° C.for 1 week. 5 Aged sandwich in oven at 140° C. for 1 week. 6 Separatelayers and measure the insulation plaque thickness. 7 At 60 Hz and 2 kV,measure the dielectric constant and dissipation factor of the insulationat room temperature, 40, 90, 110, and 130° C.

Comparative Examples 1-12 and Example 13

Comparative Example 1 represents a baseline characterization of theinsulation dielectric properties after 1 week of aging at 140° C. Theinsulation from Comparative Example 1 has not contacted a semiconductivecomposition. The 60 Hz dissipation factor does not change significantlybetween room temperature and 90° C., and is approximately 1e-4. Astemperatures increase above the melting point of the low densitypolyethylene insulation, the dissipation factor increases, and anincrease of about 1 order of magnitude is observed at 130° C. ascompared to the room temperature measurement.

In Comparative Example 2, the insulation is molded against asemiconductor formulation. The layers are separated before any thermalaging. The resulting dielectric properties of the insulation are similarto Comparative Example 1. In Comparative Example 3, theinsulation-semiconductor composite is aged prior to separation of thelayers. The dielectric properties of the insulation are notsubstantially altered at room temperature, but significantly higherlosses are experienced at higher temperatures. At temperatures of 90° C.and higher, the insulation from Comparative Example 3 exhibits adissipation factor that is approximately 20 times higher than the unagedinsulation of Comparative Example 2 or the insulation without contact tosemiconductor of Comparative Example 1. The results clearly indicatethat the method sufficiently reproduces the mechanism that led to theexperience of high dielectric losses after thermal aging in a cableconstruction using the elastomer-containing semiconductor of compositionSC-1. The results also indicate that the mechanism that leads to theincreased dielectric losses is related to the diffusion of a lossyspecies from the semiconductive material into the insulation layer.

In Comparative Examples 4 through 8, the HFDB-4202 tree-retardantinsulation formulation is employed. This is the same insulation as wasused in the cable that exhibited high dielectric losses after thermalaging.

Comparative Example 8 shows the dielectric losses after thermal aging ofthe insulation without contact with a semiconductive composition. Thedissipation factor as a function of temperature is similar to thatexhibited by the HFDE-4201 insulation of Comparative Example 1, withvalues in the range of 2e-4 to 3e-4 at 130° C.

For Comparative Examples 4 and 6, the dissipation factor of theinsulation which was molded against semiconductive compositionscontaining different elastomer content was measured prior to any thermalaging. The resulting dissipation values are similar to the unagedinsulation of Comparative Example 8.

In Comparative Examples 5 and 7, the insulation semiconductor sandwichwas thermally aged prior to the measurement of the dielectric propertiesof the insulation layer. As was observed in similar experimentation withHFDE-4201 in Comparative Example 3, the dissipation factor valuesincrease dramatically at temperatures of 90° C. and above for theinsulation of Comparative Examples 5 and 7, in which HFDB-4202insulation was aged in contact with the semiconductive compositionscontaining elastomer. The dissipation factors experienced at 130° C.were so high that there was difficulty making the dissipation factormeasurement (therefore the value is reported as “NO READING”). It can beseen, however, that the dissipation factor values at 110° C. wereapproximately 100 times that of Comparative Example 8, in which the sameinsulation was thermally aged without contact with the semiconductivecompositions.

A comparison of Comparative Example 5 to Comparative Example 7 indicatesthat the difference in the level of elastomer used in SC-2 and SC-3 wasnot significant enough to make a notable difference in thehigh-temperature dissipation factor.

The results of Comparative Examples 4 through 8 confirm that the testmethod is suitable to probe the effects of the mechanism that leads toincreased dielectric losses in thermally aged cables, and that themechanism is related to diffusion of a lossy species from thesemiconductive composition into the insulation layer.

Comparative Example 9 employs HFDE-4201 which is thermally aged againsta semiconductive composition SC-4. However, SC-4 has been formulatedwithout the presence of the propylene-ethylene elastomer. The results ofthe dielectric measurements on the insulation are similar to that ofComparative Example 1, which is the aged insulation that never contacteda semiconductive composition.

This clearly demonstrates that the elastomer is the source of thespecies which diffuses into the insulation to yield high dielectriclosses.

Comparative Examples 10 through 12 and Example 13 examine the use ofvarious fillers in the semiconductive composition in an effort to affectthe resulting dielectric performance of an insulation when thermallyaged against the semiconductive composition. Comparative Examples 10 and11 utilize semiconductive compositions SC-5 and SC-6, which containcalcium carbonate or talc. These mineral fillers have the potential toreduce diffusion rates of migrating species, and can neutralize acidicspecies that could negatively impact dielectric performance. Theresulting dielectric performance of the insulation in ComparativeExamples 10 and 11, however, was not improved relative to thehigh-losses experienced from the insulation in Comparative Example 3.

Comparative Example 12 employs semiconductive composition SC-7, in whichnatural montmorillonite clay was incorporated. Such clays have been usedto improve barrier properties (reduce diffusion). However, the resultingdielectric properties from the insulation in Comparative Example 12 arenot improved relative to the high losses experienced in ComparativeExample 3.

The present invention is exemplified in Example 13, in which thesemiconductive composition SC-8 contains an organoclay treated with anexcess of quaternary ammonium. The dissipation factor of the insulationafter thermal aging against SC-8 is substantially improved (lower) attemperatures of 90° C. and higher, relative to that of ComparativeExample 3, in which the semiconductor composition SC-1 contained noorganoclay. The use of the organoclay in the formulation of SC-8 is notsufficient to result in dissipation factor performance of the agedinsulation without contact to semiconductors, which indicates thatmigration of the lossy species from the semiconductive formulation hasbeen reduced but not completely prevented. However, it is significantthat the use of fillers at the same loading level was not effective inretarding diffusion of the lossy species.

It should be noted that exfoliation of the organoclay in the compositionis not expected.

TABLE 1 Compositions for Examples and Comparative Examples ComponentSC-1 SC-2 SC-3 SC-4 SC-5 SC-6 SC-7 SC-8 SC-9 EVA 43.6 48.6 54.6 63.647.6 47.6 47.6 47.6 47.6 PP1 18 18 12 16 16 16 16 16 Carbon Black 38 3333 36 335 35 35 35 35 Hubercarb CaCO3 1 Mistron ZSC Talc 1 Cloisite NA+1 Cloisite 15A 1 Cloisite 20A 1 AO 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4Intermediate 100 100 100 100 100 100 100 100 100 Intermediate 99.3 99.399.3 99.3 99.3 99.3 99.3 99.3 99.3 Peroxide 0.7 0.7 0.7 0.7 0.7 0.7 0.70.7 0.7 EVA 33% VA; 30 MI ethylene vinyl acetate copolymer PP1 propyleneethylene copolymer (12% et); 25 MFR; peak melting point ~80 C. CarbonBlack Low-surface area, moderate structure furnace black CaCO3 Hubercarbcalcium carbonate Talc Mistron ZSC talc Cloisite Na+ naturalmontmorillonite with Cation exchange capacity of 93meg/100 g clay; d001= 11.7 Angstroms Cloisite 15A natural montmorillonite modified with125meg/100 g clay using 2M2HT*; d001-31.5 Angstroms Cloisite 20A naturalmontmorillonite modified with 95meg/100 g clay using 2M2HT*; d001 = 24.2Angstroms *dimethyl-dihydrogentallow quaternary ammonium (chlorideanion) AO 4,4-bis(dimethyl benzyl)diphenylamine Peroxidebis(t-butylperoxy)diisopropyl benzene Insulations HFDB-4202 TR-XLPEavailable from The Dow Chemical Company HFDE-4201 XLPE available fromThe Dow Chemical Company

TABLE 2 (A) Dielectric Measurements on Insulation: Examples andComparative Examples (part A) Dielectric Measurements Comp. Comp. Comp.Comp. Comp. Comp. Comp. Comp. Example 1 Example 2 Example 3 Example 4Example 5 Example 6 Example 7 Example 8 Semicon none SC-1 SC-1 SC-2 SC-2SC-3 SC-3 none Insulation HFDE-4201 HFDE-4201 HFDE-4201 HFDB-4202HFDB-4202 HFDB-4202 HFDB-4202 HFDB-4202 140 C. aging yes no yes no yesno yes yes Dielectric Constant 2 kV, 60 Hz RT 2.176 2.159 2.087 2.2732.126 2.204 2.171 1.603  40 C. 2.18 2.152 2.114 #N/A #N/A #N/A #N/A #N/A 50 C. #N/A #N/A #N/A 2.238 2.124 2.201 2.22 2.101  70 C. #N/A #N/A #N/A2.22 2.119 2.162 2.191 2.164  90 C. 2.068 1.809 2.042 2.038 2.08 2.0482.046 2.067 110 C. 1.859 1.733 1.875 1.876 1.857 1.894 1.891 1.943 130C. 1.813 1.711 1.786 1.808 NOREADING 1.854 NOREADING 1.907 DissipationFactor 60 Hz RT 0.000118 0.000125 0.000238 0.000311 0.001128 0.0003580.000385 0.000595  40 C. 0.000089 0.000108 0.000118 #N/A #N/A #N/A #N/A#N/A  50 C. #N/A #N/A #N/A 0.000152 0.000863 0.000238 0.000212 0.000358 70 C. #N/A #N/A #N/A 0.000128 0.000709 0.000188 0.000502 0.000245  90C. 0.000125 0.000195 0.002882 0.000104 0.004656 0.000202 0.0034080.000269 110 C. 0.000714 0.000438 0.026552 0.000328 0.039538 0.0004230.082562 0.000727 130 C. 0.002512 0.001842 0.048558 0.001591 NOREADING0.001378 NOREADING 0.002438

TABLE 2 (B) Dielectric Measurements on Insulation: Examples andComparative Examples (part B) Comp. Comp. Comp. Comp. Example 9 Example10 Example 11 Example 12 Example 13 Example 14 Semicon SC-4 SC-5 SC-6SC-7 SC-8 SC-9 Insulation HFDE-4201 HFDE-4201 HFDE-4201 HFDE-4201HFDE-4201 HFDE-4201 140 C. aging yes yes yes yes yes not measuredDielectric Constant 2 kV, 60 Hz RT 2.107 2.037 2.16 2.116 2.113  40 C.2.069 2.031 2.158 2.115 2.106  50 C. #N/A #N/A #N/A #N/A #N/A  70 C.#N/A #N/A #N/A #N/A #N/A  90 C. 1.949 1.068 1.987 2.063 1.969 110 C.1.853 1.105 1.861 NOREADING 1.852 130 C. 1.801 1.164 1.336 NOREADING1.787 Dissipation Factor 60 Hz RT 0.000142 0.000118 0.000168 0.0001380.000121  40 C. 0.000118 0.000094 0.000112 0.000108 0.000092  50 C. #N/A#N/A #N/A #N/A #N/A  70 C. #N/A #N/A #N/A #N/A #N/A  90 C. 0.0000740.002826 0.005512 0.003932 0.000452 110 C. 0.000345 0.025436 0.033355NOREADING 0.003828 130 C. 0.001308 0.053439 0.062388 NOREADING 0.013652

Examples 15-18

Semiconductive compositions were prepared as shown in Table 3.

TABLE 3 Example 15 Example 16 Example 17 Example 18 Component SC-10SC-11 SC-12 SC-13 EVA 47.6 45.6 47.6 45.6 PP1 16 16 16 16 Carbon Black35 35 35 35 Cloisite 15A 1 3 Cloisite 20A 1 3 AO 0.4 0.4 0.4 0.4Intermediate 100 100 100 100 Intermediate 99.3 99.3 99.3 99.3 Peroxide0.7 0.7 0.7 0.7

Dielectric Measurements for Examples 15-18 are shown in Table 4.

TABLE 4 Example 15 Example 16 Example 17 Example 18 Semicon SC-10 SC-11SC-12 SC-13 Insulation HFDE-4201 HFDE-4201 HFDE-4201 HFDE-4201 140 C.aging yes yes yes yes Dielectric Constant 2 kV, 60 Hz RT 2.027 2.1461.897 2.131  40 C. 2.055 2.157 1.996 2.153  50 C. #N/A #N/A #N/A #N/A 70 C. #N/A #N/A #N/A #N/A  90 C. 0.818 1.695 1.992 1.985 110 C. 1.0611.871 1.882 1.894 130 C. 1.081 1.805 1.833 1.833 Dissipation Factor 60Hz RT 0.000232 0.000163 0.000228 0.000168  40 C. 0.000146 0.0001120.000176 0.000117  50 C. #N/A #N/A #N/A #N/A  70 C. #N/A #N/A #N/A #N/A 90 C. 0.000225 0.000388 0.000473 0.000228 110 C. 0.001688 0.0009040.002113 0.000586 130 C. 0.004509 0.002151 0.006507 0.001236

As was discussed relative to Example 13, the use of organoclay in thesemiconductive composition has dramatically reduced the resultinginsulation dissipation factor after the insulation and semiconductivematerials are thermally aged in intimate contact. This is again apparentwith the same organoclay in Example 15. The dissipation factor values ofExample 15 are lower than those experienced in Example 13, however, thevery low dielectric constants reported for Example 15 may suggest thatthe bridge was not properly balanced for the higher test temperatures.

Nevertheless, as can be seen in Example 16, the dissipation factorreduction effect becomes more pronounced as the organoclay content inthe semiconductor composition is increased. In Examples 17 and 18, analternate organoclay is used in the compositions, again at 1% and 3% byweight. The effect with this organoclay is similar to that of Examples15 and 16.

The results indicate that the use of approximately 3% of the organoclayscan nearly eliminate the diffusion-related dissipation factor increase.The df increases noted in a 1% organoclay loading suggested a merereduction in the rate of diffusion due to the presence of organoclay. At3% a further reduction in diffusion is expected, however, reduction ofthe df values to that experienced by systems in which no elastomer wasutilized suggest that either the timescale for diffusion at 140° C. ismuch longer than the 1-week aging time, or that there could be aphysical bond which forms between the dissipative species and theorganoclay.

The comparison of the effects of compositions prepared with organoclayswith different levels of quaternary ammonium treatment indicate that thedissipation factor reduction is not directly related to the presence ofexcess treatment.

Comparative Example 19 and 22 and Examples 20, 21, 23-26

The effect of improved (reduced) cable dielectric losses through theaddition of small amounts of organoclay in semiconductive shieldcompositions which also contain lossy elastomeric components has beendemonstrated in the previous examples. Here the investigation is taken astep further to determine if the organoclay can provide similar effectswithin a lossy insulation layer (which would demonstrate a trapping ofthe lossy species, rather than a reduction in the migration of thespecies).

An ethylene-propylene-diene elastomer has been selected for this study.This polymer is compounded with several different layers of organoclay,and with the CLOISITE® grades of organoclay with different levels ofquaternary ammonium treatment. The formulations are shown in Table 4.The results are presented in Tables 5 and 6, with graphicalrepresentation in the corresponding FIGS. 4 and 5.

The results indicate that the organoclay provides a means todramatically reduce the dielectric losses of the EPDM resin attemperatures above 100° C. Some compromise of the dielectric losses atlower temperatures is experienced. However, the magnitude of thedielectric loss for addition of low levels of organoclay represents asignificant improvement over the performance demonstrated for the EPDMwithout organoclay, for applications such as power cable insulationwhich experience use temperatures over the entire temperature rangeexamined.

The benefit of the use of organoclay in the EPDM demonstrates that theeffect in either insulating compositions or semiconductive compositions,is due to an interaction between the organoclay and the lossy specieswithin the elastomer component, and is more than a reduction inmigration of the lossy species.

TABLE 5 Compositions in wt % Comp. Ex. 19 Example 20 Example 21 EPDM 10095 90 Cloisite 20A 0 5 10 Intermediate 98.1 98.1 98.1 Dicup R 1.9 1.91.9 Sample Preparation Use Brabender to compound above compositions. Addall ingredients, achieve 90 C. melt temp. Continue to mix untiluniformly distributed. (Begin with highest clay loading to determine mixtime, then use same mixing conditions for all batches.) Add peroxide andmix for 1 additional minute. Press composition into workable form.Double-plaque each composition (do not exceed 100 C.) to remove voidsPress into a 50 mil plaque and cure at 182 C. for 15 minutes. RemoveMylar and insert into 65 C. vacuum oven for 1 week. Perform DC/DFevaluations over a range of temperatures. Test Program DC at 2 kV, 60 HzDC at RT 2.189 2.358 2.594 DC at 40 C. 2.089 2.312 2.621 DC at 90 C.1.946 2.183 2.571 DC at 130 C. 1.865 1.965 2.232 DF at 2 kV, 60 Hz DF atRT 0.000105 0.012898 0.032395 DF at 40 C. 0.000225 0.006178 0.023277 DFat 90 C. 0.004479 0.003158 0.015619 DF at 130 C. 0.020548 0.0018020.007392

TABLE 6 Compositions in wt % Comp. Ex 22 Example 23 Example 24 Example25 Example 26 EPDM 100 99 97 99 97 Cloisite 15A 1 3 Cloisite 20A 0 1 3Intermediate 98.1 98.1 98.1 98.1 98.1 Dicup R 1.9 1.9 1.9 1.9 1.9 TestProgram DC at 2 kV, 60 Hz DC at RT 2.214 2.218 2.281 2.231 2.272 DC at40 C. 2.063 2.097 2.231 2.111 2.212 DC at 90 C. 1.982 2.017 2.134 2.0082.084 DC at 130 C. 1.883 1.911 2.048 1.911 1.977 DF at 2 kV, 60 Hz DF atRT 0.000068 0.002096 0.008807 0.001946 0.005795 DF at 40 C. 0.0001490.001808 0.009076 0.003462 0.007012 DF at 90 C. 0.000922 0.0012220.006345 0.000988 0.003967 DF at 130 C. 0.016897 0.001924 0.0042590.001102 0.002238

Although the invention has been described in considerable detail by thepreceding specification, this detail is for the purpose of illustrationand is not to be construed as a limitation upon the following appendedclaims. All U.S. patents, allowed U.S. patent applications and U.S.Patent Application Publications are incorporated herein by reference.

We claim:
 1. A layered structure comprising: a semiconducting layercomprising a first material that comprises a first polymeric resin and aconductive filler, wherein the first polymeric resin comprises at leastone propylene copolymer which is a copolymer of propylene with anα-olefin comonomer, the propylene copolymer comprising lossy species;and an insulating layer consisting of a second material, the secondmaterial consisting of (a) a second polymeric resin consisting of apolyethylene crosslinked with dicumyl peroxide, and (b) an organoclay,wherein the organoclay is present and in an amount of up to 3 wt %,based on the total weight of the polymeric resin in the second material,wherein the semiconducting layer and the insulating layer are at leastpartially in physical contact with each other, and wherein the ratio ofAC dielectric losses of a comparative structure to the layered structureis greater than 1.5, after aging at 140° C. for one week, when measuredat a temperature of 130° C. and a frequency of 60 Hz, the comparativestructure being identical to the layered structure except that thecomparative structure lacks organoclay.
 2. The layered structure ofclaim 1 wherein the first polymeric resin further comprises at least oneethylene homopolymer and/or ethylene copolymer.
 3. The layered structureof claim 2 wherein the ethylene copolymer is a copolymer of ethylenewith an α-olefin or with a vinyl acetate comonomer.
 4. The layeredstructure of claim 1 wherein the conductive filler comprises at leastone carbon black compound.
 5. The layered structure of claim 1 whereinthe organoclay is a natural montmorillonite modified with a quaternaryammonium compound.
 6. The layered structure of claim 1 wherein the firstpolymeric resin is a thermoplastic resin.
 7. The layered structure ofclaim 1 wherein the first material comprises: the first polymeric resincomprising the at least one propylene copolymer and an ethylene/vinylacetate copolymer; the conductive filler comprising at least one carbonblack compound; from 1 wt % to 3 wt % organoclay, based on the totalweight of the polymeric resin in the first material; andbis(t-butylperoxy)diisopropyl benzene.
 8. A cable comprising: (i) a corecomprising one or more conductors; and (ii) a layered structurecomprising a semiconducting layer comprising a first material thatcomprises a first polymeric resin and a conductive filler, wherein thefirst polymeric resin comprises at least one propylene copolymer whichis a copolymer of propylene with an α-olefin comonomer, the propylenecopolymer comprising lossy species; and an insulating layer consistingof a second material consisting of (a) a second polymeric resinconsisting of a polyethylene crosslinked with dicumyl peroxide; and (b)an organoclay, wherein the organoclay is present and in an amount of upto 3 wt %, based on the total weight of the polymeric resin in thesecond material; wherein the semiconducting layer and the insulatinglayer are at least partially in physical contact with each other,wherein the ratio of AC dielectric losses of a comparative structure tothe layered structure is greater than 1.5, after aging at 140° C. forone week, when measured at a temperature of 130° C. and a frequency of60 Hz, the comparative structure being identical to the layeredstructure except that the comparative structure lacks organoclay; andwherein the semiconducting layer and the insulating layer directly orindirectly surround the core.
 9. The cable of claim 8 wherein the firstmaterial comprises: the first polymeric resin comprising the at leastone propylene copolymer and an ethylene/vinyl acetate copolymer; theconductive filler comprising at least one carbon black compound; from 1wt % to 3 wt % organoclay, based on the total weight of the polymericresin in the first material; and bis(t-butylperoxy)diisopropyl benzene.10. The cable of claim 8, wherein the organoclay is a naturalmontmorillonite modified with a quaternary ammonium compound.
 11. Thecable of claim 8 wherein the first polymeric resin further comprises atleast one ethylene homopolymer and/or ethylene copolymer.
 12. The cableof claim 8 wherein the conductive filler comprises at least one carbonblack compound.
 13. The cable of claim 8 further comprising a pluralityof neutral copper wires wrapped around the insulating layer, theplurality of neutral copper wires forming concentric helices.